Here's why:
* Shared Hydraulic Fluid: The power steering pump uses hydraulic fluid to assist steering. Many vehicles, including the Astro van, use the same hydraulic fluid reservoir for both power steering and the power brake booster. If the pump fails catastrophically (e.g., seizes, leaks internally, or the belt breaks), it can deplete the fluid reservoir, leaving both systems without the necessary hydraulic pressure to function.
* Possible Scenarios:
* Pump Seizure/Failure: The pump itself might have failed internally, preventing fluid from circulating.
* Leaks: A significant leak in the pump, hoses, or lines connected to the pump will drain the fluid, affecting both systems.
* Belt Breakage: The serpentine belt drives the power steering pump. If the belt breaks, both systems will fail.
* Reservoir Leak: Though less likely to cause both systems to fail simultaneously, a large leak in the reservoir would quickly drain the fluid, affecting both the power steering and brakes.
Important Note: While this is the most likely scenario, it's crucial to have a qualified mechanic diagnose the problem. There's always a chance of other, less common issues. Driving a vehicle with failing brakes is extremely dangerous. Do not attempt to drive the van until it's been properly inspected and repaired.
